Integration Techniques, L’Hôpital’s Rule, and Improper Integrals Copyright © Cengage Learning. All rights reserved.

Indeterminate Forms and L’Hôpital’s Rule Copyright © Cengage Learning. All rights reserved.

Objectives Recognize limits that produce indeterminate forms. Apply L’Hôpital’s Rule to evaluate a limit.

Indeterminate Forms

Indeterminate Forms The forms 0/0 and are called indeterminate because they do not guarantee that a limit exists, nor do they indicate what the limit is, if one does exist. When you encountered one of these indeterminate forms earlier in the text, you attempted to rewrite the expression by using various algebraic techniques.

Indeterminate Forms Occasionally, you can extend these algebraic techniques to find limits of transcendental functions. For instance, the limit produces the indeterminate form 0/0. Factoring and then dividing produces

Indeterminate Forms Not all indeterminate forms, however, can be evaluated by algebraic manipulation. This is often true when both algebraic and transcendental functions are involved. For instance, the limit produces the indeterminate form 0/0. Rewriting the expression to obtain merely produces another indeterminate form,

Indeterminate Forms You could use technology to estimate the limit, as shown in the table and in Figure 8.15. From the table and the graph, the limit appears to be 2. Figure 8.15

L’Hôpital’s Rule

L’Hôpital’s Rule To find the limit illustrated in Figure 8.15, you can use a theorem called L’Hôpital’s Rule. This theorem states that under certain conditions, the limit of the quotient f(x)/g(x) is determined by the limit of the quotient of the derivatives Figure 8.15

L’Hôpital’s Rule To prove this theorem, you can use a more general result called the Extended Mean Value Theorem.

L’Hôpital’s Rule

Example 1 – Indeterminate Form 0/0 Evaluate Solution: Because direct substitution results in the indeterminate form 0/0.

Example 1 – Solution You can apply L’Hôpital’s Rule, as shown below. cont’d You can apply L’Hôpital’s Rule, as shown below.

L’Hôpital’s Rule The forms have been identified as indeterminate. There are similar forms that you should recognize as “determinate.” As a final comment, remember that L’Hôpital’s Rule can be applied only to quotients leading to the indeterminate forms 0/0 and

L’Hôpital’s Rule For instance, the following application of L’Hôpital’s Rule is incorrect. The reason this application is incorrect is that, even though the limit of the denominator is 0, the limit of the numerator is 1, which means that the hypotheses of L’Hôpital’s Rule have not been satisfied.